bwt locate

bwt/bwt.go

@@ -13,25 +13,48 @@ const nullChar = "$"
 // allows for sub sequence querying.
 type BWT struct {
 	skipList []skipEntry
-	l        waveletTree
+	// TODO: talk about how we would want to remove this in favor of a RLFM and or r-index
+	l waveletTree
+	// TODO: Talk about how we can cut way down on memory usage by sampling this in a specific way with the RLFM and or r-index
+	suffixArray []int
 }
 
 func (bwt BWT) Count(pattern string) int {
+	searchRange := bwt.lfSearch(pattern)
+	return searchRange.end - searchRange.start
+}
+
+func (bwt BWT) Locate(pattern string) []int {
+	searchRange := bwt.lfSearch(pattern)
+	if searchRange.start >= searchRange.end {
+		return nil
+	}
+
+	numOfOffsets := searchRange.end - searchRange.start
+	offsets := make([]int, numOfOffsets)
+	for i := 0; i < numOfOffsets; i++ {
+		offsets[i] = bwt.suffixArray[searchRange.start+i]
+	}
+
+	return offsets
+}
+
+func (bwt BWT) lfSearch(pattern string) interval {
 	searchRange := interval{start: 0, end: bwt.getLenOfOriginalString()}
 	for i := 0; i < len(pattern); i++ {
 		if searchRange.end-searchRange.start <= 0 {
-			return 0
+			return interval{}
 		}
 
 		c := pattern[len(pattern)-1-i]
 		skip, ok := bwt.lookupSkip(c)
 		if !ok {
-			return 0
+			return interval{}
 		}
 		searchRange.start = skip.openEndedInterval.start + bwt.l.Rank(c, searchRange.start)
 		searchRange.end = skip.openEndedInterval.start + bwt.l.Rank(c, searchRange.end)
 	}
-	return searchRange.end - searchRange.start
+	return searchRange
 }
 
 func (bwt BWT) lookupSkip(c byte) (entry skipEntry, ok bool) {
@@ -67,19 +90,23 @@ func New(sequence string) BWT {
 
 	slices.Sort(prefixArray)
 
+	suffixArray := make([]int, len(sequence))
 	lastColBuilder := strings.Builder{}
 	for i := 0; i < len(prefixArray); i++ {
 		currChar := sequence[getBWTIndex(len(sequence), len(prefixArray[i]))]
 		lastColBuilder.WriteByte(currChar)
+
+		suffixArray[i] = len(sequence) - len(prefixArray[i])
 	}
 	fb := strings.Builder{}
 	for i := 0; i < len(prefixArray); i++ {
 		fb.WriteByte(prefixArray[i][0])
 	}
 
 	return BWT{
-		skipList: buildSkipList(prefixArray),
-		l:        NewWaveletTreeFromString(lastColBuilder.String()),
+		skipList:    buildSkipList(prefixArray),
+		l:           NewWaveletTreeFromString(lastColBuilder.String()),
+		suffixArray: suffixArray,
 	}
 }
 

bwt/bwt_test.go

@@ -3,19 +3,20 @@ package bwt
 import (
 	"strings"
 	"testing"
+
+	"golang.org/x/exp/slices"
 )
 
 type BWTCountTestCase struct {
 	seq      string
 	expected int
 }
 
-const augmentedQuickBrownFoxTest = "thequickbrownfoxjumpsoverthelazydogwithanovertfrownafterfumblingitsparallelogramshapedbananagramallarounddowntown"
-
-var threeAugmentedQuickBrownFoxTest = strings.Join([]string{augmentedQuickBrownFoxTest, augmentedQuickBrownFoxTest, augmentedQuickBrownFoxTest}, "")
-
 func TestBWT_Count(t *testing.T) {
-	bwt := New(threeAugmentedQuickBrownFoxTest)
+	baseTestStr := "thequickbrownfoxjumpsoverthelazydogwithanovertfrownafterfumblingitsparallelogramshapedbananagramallarounddowntown"
+	testStr := strings.Join([]string{baseTestStr, baseTestStr, baseTestStr}, "")
+
+	bwt := New(testStr)
 
 	testTable := []BWTCountTestCase{
 		{"uick", 3},
@@ -38,6 +39,44 @@ func TestBWT_Count(t *testing.T) {
 	}
 }
 
+type BWTLocateTestCase struct {
+	seq      string
+	expected []int
+}
+
+func TestBWT_Locate(t *testing.T) {
+	baseTestStr := "thequickbrownfoxjumpsoverthelazydogwithanovertfrownafterfumblingitsparallelogramshapedbananagramallarounddowntown" // len == 112
+	testStr := strings.Join([]string{baseTestStr, baseTestStr, baseTestStr}, "")
+
+	bwt := New(testStr)
+
+	testTable := []BWTLocateTestCase{
+		{"uick", []int{4, 117, 230}},
+		{"the", []int{0, 25, 113, 138, 226, 251}},
+		{"over", []int{21, 41, 134, 154, 247, 267}},
+		{"own", []int{10, 48, 106, 110, 123, 161, 219, 223, 236, 274, 332, 336}},
+		{"ana", []int{87, 89, 200, 202, 313, 315}},
+		{"an", []int{39, 87, 89, 152, 200, 202, 265, 313, 315}},
+		{"na", []int{50, 88, 90, 163, 201, 203, 276, 314, 316}},
+		{"rown", []int{9, 47, 122, 160, 235, 273}},
+		{"townthe", []int{109, 222}},
+		{"zzz", nil},
+	}
+
+	for _, v := range testTable {
+		offsets := bwt.Locate(v.seq)
+		slices.Sort(offsets)
+		if len(offsets) != len(v.expected) {
+			t.Fatalf("seq=%s expectedOffsets=%v actualOffsets=%v", v.seq, v.expected, offsets)
+		}
+		for i := range offsets {
+			if offsets[i] != v.expected[i] {
+				t.Fatalf("seq=%s expectedOffsets=%v actualOffsets=%v", v.seq, v.expected, offsets)
+			}
+		}
+	}
+}
+
 func BenchmarkBWTBuildPower12(b *testing.B) {
 	base := "!BANANA!"
 	BaseBenchmarkBWTBuild(base, 12, b)